Otitis media and other illnesses caused by nontypable Haemophilus influenzae (NTHI) remain significant health problems for children in this country and elsewhere in the world. The long-term objectives of this project are to identify those surface-exposed bacterial antigens of NTHI that are important in a protective host immune response and ultimately to address the question of whether or not a vaccine composed of such antigens would be effective in the prevention of disease. In previous work, we identified the HMW1/HMW2 family of proteins as major targets of the human serum antibody response following natural infection and colonization. Furthermore, we demonstrated a critical role for these proteins in adhesion of NTHI to eukaryotic cells. With respect to the potential of these proteins as vaccine candidates, we demonstrated that immunization of chinchillas with an HMW1/HMW2 mixture provided protection against experimental NTHI otitis media caused by the homologous strain. Finally, in our preliminary studies, we demonstrated that adult human serum antibodies specific for the HMW1/HMW2 family of proteins mediate opsonophagocytic activity against both homologous and heterologous strains. We propose to build on these earlier studies with the following specific aims. We will characterize the contribution of antibodies produced against the HMW1/HMW2- like proteins to the opsonophagocytic activity that develops in convalescent sera of children with acute NTHI otitis media. We will map those regions of the HMW1/HMW2-like proteins that express epitopes recognized by antibody capable of mediating opsonophagocytic activity against both homologous and heterologous strains. Finally, we will assess the ability of recombinant proteins that express epitopes recognized by antibodies mediating opsonophagocytic activity against homologous and heterologous strains to provide protection against disease in the chinchilla model of experimental NTHI otitis media. The knowledge gained from these studies will provide a clearer picture of the role of antibody to the HMW1/HMW2 proteins in host immunity and may move us closer to the goal of developing vaccines for prevention of nontypable Haemophilus influenzae otitis media and other diseases in young children.